Radical thought- Use 2 pair of speakers

Each pair has (its) own unique characteristics to why not add them together

Because most likely you'll have more of cancellation and addition than complementarity, resulting in nulls & humps.
But... you never know!

Seems like it would be hard to get them to image well with such a large baffle area. (I guess I assumed you meant they would sit side by side?)

You are forgetting that benefits are not always additive. Sub woofers have long wavelengths, which are not directional to our ears, and hence can be additive. Mid range and tweeter frequencies are not additive....the result will be excessive comb filtering or a vague atmospheric sound that totally lacks focus. Even on a surround system the speakers should all match in timbre and characteristics (means you should really use the same speakers to get the most benefit).

Surround sound only works because the speakers are separated distinctly and the channel information fed to each speaker is specific for that arrangement, including delay adjustments according to specific speaker/listener positions.

Many recoriding studios use two different sets of monitors at once. If it works it works...

DV

DV, maybe that's why there are so many bad recordings..